Optical logic gates have been the subject of research for several decades due to the possibility of achieving higher operating speeds than logic based on electronics. The advantages of digital signal processing in the optical domain include higher signal bandwidth, lower signal cross-talk, and greater protection against electronic eavesdropping. All-optical signal processing also eliminates the need to convert signals from the optical domain into the electronic domain for processing using electronic signal processing circuitry, and then to re-convert the processed signals from the electronic domain back into the optical domain. All-optical signal processing is advantageous to reduce the cost, electrical power requirement, size and weight compared to optical-to-electronic converters, electronic signal processing circuitry, and electronic-to-optical converters which are currently being used.
In the development of optical signal processing, there is a need for optical memory to store the optical information being processed. Prior digital optical logic gates have been incapable of storing the optical information being processed and thus have operated asynchronously. Such asynchronous operation is undesirable since it does not allow the transfer of the optical information from one optical logic gate to another using an optical clock pulse.
The present invention addresses this need by providing an optical data latch that can be used to store a bit of optical information in digital optical form. The optical data latch of the present invention can also be used to form a clocked optical data shift register which operates synchronously to store many bits of optical information, and to read those bits of optical information into and out of the shift register using an optical clock.
The optical data latch of the present invention utilizes two optical logic gates in a cross-coupled arrangement to provide a bi-stable operation which can be used to optically store a logical “0” state or a logical “1” state in the latch. Each optical logic gate, which can be either an optical NOT gate (also termed an optical inverter) or an optical NOR gate, comprises a single waveguide electroabsorption modulator which is electrically connected in series with a waveguide photodetector. A resistor can also be connected in parallel with the waveguide electroabsorption modulator to increase the operating speed of the optical data latch. The optical data latch operates using optical input signals to set or reset an optical logic state (i.e. a bit of optical information) in the latch, and can also provide that optical logic state and its complement as optical output signals from the latch. Only direct current (dc) electrical power sources are required to operate the optical data latch, with these dc power sources being used to bias the waveguide photodetector and waveguide electroabsorption modulator, to operate one or more semiconductor lasers to generate light which is used to store the bit of optical information within the latch, and to operate optional semiconductor optical amplifiers which can be used to provide optical signal gain and regeneration in the latch.
These and other advantages of the present invention will become evident to those skilled in the art.